Vaccines

       

                            Vaccines:

What is vaccine?

A vaccine is a biological preparation that improves immunity to a specific disease.

A Vaccine generally contains an agent that resembles a disease causing microorganism and it is often made from weekend or

killed from of the microbe.

The term vaccines has been derived from the Latin word meaning from cows.

                Who discovered vaccine?

Edward Jenner is considered the inventor of vaccines. In 1798 the first smallpox vaccine was developed by Edward Jenner.

                     What is vaccination?

Vaccination means that a biological method of giving antigen to stimulate the the immune response through active immunization.

A vaccine is an immuno- biological substance designs to to produce specific protection against a given disease.

A vaccine is "antigenic" but not "pathogenic"

Types of antigens used in vaccine preparation:

Vaccine can be prepared from whole organisms to small subcellular fragment  used as antigen in vaccines.

Most recent vaccine in use for humans mainly consists of of whole organism which included with live but attenuated vaccines or killed organisms and purified antigen vaccines ( toxoids, capsular polysaccharide and recombinant microbial antigens). Recent advances in molecular biology had provided alternative methods for producing vaccines such as DNA vaccines and recombinant vector vaccines.

Whole organism vaccines:

It included with two categories

I) live but attenuated.

II) inactivated or killed vaccines.

I) Live but attenuated:

This type of vaccines are prepared by attenuating pathogenic organisms by growing them in an unfavourable conditions which turns to result in genetic mutation due to which organisms  looses pathogenicity but retain their capacity for transient growth.

Virulent  pathogenic organisms are treated to become attenuated  and avirulent but antigenic. Generally they have lost their capacity to induce full-blown disease but retain their immunogenicity.

Live attenuated vaccines should not be administrated two persons with suppress immune response due to

Leukaemia

Receiving corcosteroids and metabolic agents.

Radiation.

Pregnancy.

II) Inactivated or killed vaccines:

Inactivated vaccines can be produced by inactivation of pathogenic organisms by heat or chemical treatment so that organisms are unable to multiply  in host body. Inactivation is carried out in such a way so that the structure of epitopes on surface antigen remain maintained. Hence heat treatment is generally not satisfactory since it can cause protein degradation and thus loss of some epitopes. In case of chemical inactivation using formaldehyde or other alkylating agent is  more common. Inactivated vaccines  are effective but they are less immunogenic so often require several boosters and normally do not adequately stimulate cell mediated immunity or secretory IGa production.

                         Comparison:

Sub           Attenuated               Inactivated

Booster         single                           multiple

Stability          less                              more

stable

Immunity    Humoral and                Mainly

Induced        cell mediated               humoral

Riversion     May revert to       can not revert

to virulent   a virulent form   

Form

                            

Purified antigen vaccine:

Purified antigen vaccine also known as vaccine consist of macromolecule purifier directly from the pathogen.

It consists only and unique parts of the pathogen which are necessary to elecit a protective immune response.

In some cases vaccines are epitopes the very specific part of antigen that antibodies or T-cell recognise and bind to.

Example: plague immunization.

The three most common available subunit vaccines are

I) oxides are in activated exotoxins.

II)capsular polysaccharides orsurface glycoprotein.

III) Recombinant microbial antigen.

Toxoids:

Mini exotoxins can be modified chemically so they retain their antigenicity but they are no longer toxic. Such as modified form is known as Toxoid.

Toxoids are usually not as efficient as the original exotoxin for producing immunity but they can be given safely and in high doses.

A vaccine in made from a toxin that has been made harmless but that illicit and immune response against the toxin.

Best on the Based on the  prepared by certain bacteria ( e.g tetanus or diptheria ). Vaccines are can be used when a bacterial toxins are the main reason of illness.

Bacterial toxins are in activated by heat treatment them with formalin (a solution of formaldehyde and sterilized water).

Shortly detoxified toxins are called toxoids and these are safe for use as a vaccine. Toxoid vaccines are in activated exotoxins.

When the immune system receives a vaccine containing a harmless toxoid, it learns how to fight of the natural toxin.

The immune system produces antibodies that lack out and block the toxin.

Example: vaccine against diphtheria and tetanus are example of toxoid vaccines.

Capsular polysaccharides:

The violence of some pathogenic bacteria depends primarily on the enter phagocytic properties of their polysaccharide capsule. Coating the capsule with antibodies and for complement generally greatly increases the ability of macrophages and neutrophils to phagocytosis search pathogen. The recent vaccine for streptococcus pneumonia composed of 13 antigenically distinct capsular  polysaccharide ( PCV13). The vaccine generally induces the formation of option nising antibodies and it is on the the list of vaccine recommended for all new bornes. the vaccine for neisseria meningitidis is a common cause of bacterial meningitidis also consist of free fire capsular  polysaccharides.

Recombinant antigen vaccine:

In the case of Recombinant antigen vaccine, the gene encoding any immunogenic protein can be cloned and expressed in bacterial, yeast or mammalian cells using  recombinant DNA technology. The first recombinant antigen vaccine approved for human use is the hepatitis B vaccine. The immune response which is generated by recombinant antigen vaccine is generally humoral.

DNA vaccines:

DNA vaccines also known as genetic vaccines. In this procedure use the genetic material of the pathogen itself to immunize the individual. Fragments of the pathogen's genome encoding antigenic proteins  are injected directly into the host cells where they can accumulate into the chromosomal DNA or exist as episomes.

A DNA vaccine against microbe would evoke a strong antibody response to the free floating antigen secreted by cells and the vaccine also would simulate a strong cellular response against the microbial antigens displayed on the cell surface.

DNA vaccine can not cause any disease because they do not contain the microbe, just a few copies of a genes.

DNA vaccine hard relating easy and inexpensive to design and procedure.

Naked DNA vaccines are being tested in humans inducing those against  the viruses cause influenza and herpes.

Uses of DNA vaccines have some advantages and disadvantages:

Advantages: 

It is very stable, it resists  temperature and hence storage and  transports are very easy.

Sequence can be changed with easily in laboratory.

There is no protein complement and so there will be no immune response against the vector itself.

Inserted DNA does not replicate and encodes only the protein of interest.

Disadvantages:

Potential integration of DNA into host genome main cause leading to insertional mutagenesis.

The expression of the antigen in the host may lead to specific non responsiveness to that antigen.

Recombinant vector vaccines jeans that encode antigen which is is isolated from a pathogen can be administrated into nonvirulent viruses or bacteria.

Vectors refers to the virus or bacteria as the carrier.

Viruses binds to cells and inject their genetic material into them.

A number of organisms have been used for vector vaccines such as vaccinia virus,the canary pox virus , attenuated polio virus and etc. The antigen elicit humoral immunity as well as cellular immunity.

Conjugate vaccine:

Polysaccharides coating disguise a bacterium's antigen so that the immature immune system of infants and younger children can't recognise or respond to them.

Example: Haemophilus, Influenza type B vaccine.

Vaccine adjuvant:

Vaccine adjuvant means that a substance is added to a vaccine to increasing the body's immune response to the vaccine.

Example: Saponin.

Saponins are natural glycosides of steroid or triterpine which exhibited many different biological and pharmological activities. Saponin can also activate the mammalian immune system ,which have lead to significant interest in their potential as vaccine adjuvants.

Some vaccines for infectious disease in humans:

Bacterial Diseases:     Types of vaccine used:

Diptheria                        Toxoid

Typhoid.                    Killed bacteria
                                    (Salmonella typhi)

Cholera                          killed cells
                                  ( Vibrio cholerae )

Tuberculosis            Attenuated strain of
                           Mycobacterium tuberculosis
                                           ( BCG )


Viral Diseases:         Types of vaccine used


Polio                        Attenuated Virus ( Sabin )
                                               or
                                   Inactivated virus ( Salk )


Influenza                    Inactivated virus

Smallpox                     Cross- reacting virus
                                          ( Vaccinia )

Varicella                        Attenuated virus
( chickenpox)